Modular Structures

L & I frequently receives inquiries regarding “tiny homes” and questions about the rules and requirements that apply to them. Normally, a “tiny home” is occupied and used as a dwelling, in which case it is a building regulated by the state building code. The exemption in the building code for small sheds and accessory structures does not apply to a structure used as a dwelling.

Tiny homes constructed on site are regulated by the local building department and electrical program. A tiny home constructed off site and shipped to a location in Washington State, is a modular building regulated as a “factory built structure” under RCW 43.22 and WAC 296-150F by the L & I factory Assembled Structures (FAS) program. All factory-built structures must meet the relevant provisions of the current state building and electrical codes.

If the “tiny home” is; less than 400 square feet, mounted on a permanent chassis, and used for temporary recreational purposes such as a lake cabin, then it may be a Park Model Recreational Vehicle (PMRV), also knows as a Recreational Park Trailer (RPT). PMRV’RPT’s are constructed to the national consensus standard ANSI A119.5 and are designed only for “temporary recreational purposes”. They are not intended or approved to be used as a dwelling or home. Installation and use of recreational units is subject to local zoning and land use regulations. There is an exception in state law, RCO 36.01.225 that allows a PRMV/RPT to be used as a residence if it is located in a manufactured/mobile home community, ad defined in RCO 59.20.030 and is hooked up to utilities.(Back to Top)